Members of the military, fire fighting personal, and others who are required to operate in extreme temperature environments, for example, in the desert, near fires, or at latitudes approaching the Polar Regions, frequently rely on garments that have heat exchanging liquids flowing therethrough in order to maintain a safe body temperature. In addition, workers in hazardous chemical, thermal and manufacturing environments must wear personal protective equipment (PPE) to minimize their exposure to hazardous substances, however, the PPE can limit the body's ability to shed excess heat. Flexible heat exchangers have proven to be one of the most effective methods of adding or extracting heat from the human body. These garments include flexible tubing that is sewn into the garment to carry cooling or heating fluids in close contact with the wearer's body. In general, heating or cooling garments are exemplified by U.S. Pat. Nos. 3,451,812; 3,425,486; 3,419,702; 4,691,762; 4,718,429; and 4,998,415. Other types of systems for body heating and cooling are illustrated in U.S. Pat. Nos. 4,114,620 and 5,062,424.
Most commonly, the tubing used in heat exchanging garments is standard, rigid PVC, which can be attached to the base fabric using any of three methods. The first and most common uses a standard zig-zag sewing machine with a custom foot to keep the tubing centered. The second method, which was introduced by NASA, uses a base garment formed from a mesh material with the tubing “woven” through the fabric. The third and most current method was developed at the U.S. Army Garrison-Natick. This microclimate cooling garment (MCG), which is described in U.S. Pat. No. 5,320,164 of Szczesuil, et al., uses specialty tooling and fabric to create a two layer lamination with the PVC tubing locked between the layers in a complex pattern employing ten separate flow circuits. The Natick technology is the most widely deployed to date.
No matter which construction method is used, all require the use of manifolds or miniature fittings to create individual flow circuits, thus minimizing back pressure and optimizing heat transfer. Manifolds that are currently in use are typically made from rigid polymers, such as polyamides, e.g., NYLON®. Most cooling garments use miniature barbed fittings that are inserted into the ends of the flexible tubing. Examples of the barbed fittings of the type used in the Natick MCG are shown in FIGS. 1a-1c. FIG. 1c illustrates a typical prior art tubing/manifold assembly with two four-port manifolds 2 and 4, for connection to inlet line 14 and outlet line 18, respectively, via barbed fittings 12 and 16. Manifold 2 has four ports 6a-6d, the barbed ends of which insert into tubes 8a-8d, respectively. The outlet ends of tubes 8a-8d are fitted over ports 10a-10d of manifold 4 after which the flexible tubing 8a-8d is secured to the manifold using a cyanoacrylate adhesive and a NYLON® cable tie (not shown). (The soft PVC tubing will not form a watertight seal unless an adhesive or sealant is used when joining the tubing to the manifold. Because there is considerable mechanical stress on the joint, the adhesive/sealant is prone to failure and a secondary clamp, such as a cable tie, must be used to minimize failures.) FIG. 1a illustrates an exemplary MCG rigid manifold which has a barbed inlet/outlet fitting 22, a distribution chamber 20 and a plurality of fittings 24a-24j which are dimensioned for insertion into the ends of flexible tubing (not shown). Whether discrete fittings or complex manifolds are used in heat transfer garments, there are two common issues: both are formed from rigid plastic, and both use hose barbs to secure the tubing. Details of a small section of a prior art rigid manifold are provided in FIG. 1b to illustrate the significant reduction in inner diameter at the hose barbs, which impairs the performance of the garments due to the reduced liquid flow (increased back pressure) at both the input and output manifolds. In the illustrated example, the inner diameter of inlet/outlet fitting 22 is 0.182 in. (4.62 mm) while the supply/return tubing has an inner diameter of 0.1875 in. (4.76 mm). At the tube fittings 24a-24j, each fitting has an inner diameter of 0.070 in. (1.78 mm), while the flexible tubing that runs through the garment has an inner diameter of 0.096 in. (2.4 mm). Thus, the manifold hose barb reduces the cross-sectional area of the supply/return tubing by ˜10% to ˜50% of the garment tubing.
Incompatibility in durometer (hardness) between the rigid manifold material and the flexible PVC tubing can produce a weaker joint. However, if the same fitting configuration were to be fabricated using PVC resin, it would require a thicker cross-section to achieve a strength similar to the current rigid polymer version. Additional drawbacks of such designs include the lack of conformability to the natural curvatures and movements of the human body, which can introduce strain on the tubing due to increased flexing near the manifold connections, increased garment wear near the location of the manifold, and possible discomfort for the user.
Accordingly, the need remains for fittings for effectively and efficiently connecting tubing to and within heat exchanging garments without negatively impacting their comfort and wear. The present invention is directed to such fittings and manifolds formed therefrom.